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Friday, April 16, 2010

Reading i18n messages from the database with Grails

In a recent consulting engagement, a client wanted to know how to go about reading i18n messages from the database rather than static properties files (the default in Grails). Considering how easy this is to do I was surprised when I Googled it that there was no information on how this is achieved.

Anyway it's dead simple. Just create a domain class that models a message:

class Message {

String code

Locale locale

String text

}

Then implement a class that extends the org.springframework.context.support.AbstractMessageSource class. In the example below I am using simple GORM finders to lookup a message using the code and locale

class DatabaseMessageSource extends AbstractMessageSource {

protected MessageFormat resolveCode(String code, Locale locale) {

Message msg = Message.findByCodeAndLocale(code, locale)

def format

if(msg) {

format = new MessageFormat(msg.text, msg.locale)

}

else {

format = new MessageFormat(code, locale )

}

return format;

}

}

Then wire it in using Spring by configuring a "messageSource" bean in the grails-app/conf/spring/resources.groovy file:

beans = {

messageSource(DatabaseMessageSource)

}

And that's it. Now you're serving messages from the database. Of course this is a terrible inefficient implementation since we're hitting the database for ever message code used in the application. However, it's pretty easy to introduce caching. Just create a cache key:

@Immutable

class MessageKey implements Serializable {

String code

Locale locale

}

Then configure an appropriate cache bean (I'm using Ehcache) in Spring and wire it into your MessageSource: